This invention relates to grinding blast furnace slag and more particularly to the use of an additive for improving the efficiency of the grinding operation as well as improving characteristics of the ground slag product.
Granular blast furnace slag is produced by air and water quenching of the molten, non-metallic residue remaining after the treatment of metallic ore in a blast furnace in the production of iron and steel. Grinding of such slag, followed by exposure to the proper catalyst such as lime, will produce a product which acts as a cementitious material, but only behaves well as such when ground to a very fine particle size.
The grinding of any solid material to obtain a desired finer particle size involves the consumption often times of a considerable amount of energy by the grinding equipment. It is desirable in this grinding therefore to have as efficient an operation as possible.
It has become customary in grinding products which are used in relatively large volume such as Portland cement to employ chemical "grinding aids". Such grinding aids are added before or during the grinding operation to assist in the grinding operation either by increasing the rate of production, or by increasing the fineness of the cement particles at the same rate of production, without having adverse effects on any of the properties of the ground product. In some instances, the presence of the grinding aid in the finished, ground product will also cause the ground product to exhibit a reduced tendency to compact or to "pack set". The tendency of ground solids to compact or "pack set" is thought to be brought about by cleavage of the particles during grinding of such, which exposes fresh or nascent surfaces which have high energy. Reduction of this tendency to "pack set" or compact is desirable since it facilitates the transportation of the ground product.
Many chemicals and combinations thereof have been suggested for use as grinding aids in the reduction of the particle size of Portland cement clinker and other hydraulic cements, as well as other "minerals". Some examples of grinding aids which have been successfully utilized on a commercial scale in the grinding of Portland cement clinker are phenol, acetic acid, amines and salts thereof, glycols, and combinations of the foregoing. U.S. Pat. No. 3,329,517 to Serafin discloses amine salts of acetic acid as grinding aids for Portland cement. U.S. Pat. No. 3,607,326 to Serafin discloses a grinding aid and pack set inhibitor for Portland cement and other "minerals" which is an amine salt of an aryl hydroxy compound, for example, triethanolammonium phenoxide. This patent also mentions the use of such amine salts as useful in the grinding of phosphate rock, iron ore, bauxite, clay, gypsum, amorphous silica, limestone, beryllium oxide and magnesia. The use of amine salts of alkyl benzene sulphonic acid and the diethanolamine salt of dodecyl benzene sulphonic acid in particular have been suggested as grinding aids for cements (Japanese Pat. Nos. 7421408 and 7421410 to H. Miyairi and M. Nakano). In my copending application U.S. Ser. No. 218,230 filed Dec. 19, 1980, abandoned in favor of continuation application U.S. Ser. No. 367,658, filed Apr. 12, 1982, amine salts described by Serafin in the above U.S. Pat. No. 3,607,326 are disclosed as particularly good grinding aids in the grinding of blast furnace slag. In my copending application U.S. Ser. No. 269,077 filed June 2, 1981, the use of amine salts of aromatic group-containing carboxylic acids are disclosed as effective grinding aids in the grinding of Portland cement clinker.